Fuel injection system for internal combustion engines

ABSTRACT

A fuel injection system for internal combustion engines wherein two factors determining the fuel quantity delivered to an internal combustion engine, i.e., the intake manifold vacuum in the engine and the engine rpm are converted into electrical signals having values corresponding to those of the intake manifold vacuum and the engine rpm, and the signals as well as a time interval signal (sawtooth wave) generated at the beginning of fuel injection are applied to the input of a level discrimination circuit such that the solenoid valves are held open up to the time when the sum of the applied signals reaches a discrimination level so as to inject fuel into the internal combustion engine as a function of time, characterized in that the rate of change of the time interval signal is varied according to a predetermined time lapse to thereby correct the fuel supply characteristics.

llnite States Patent 1191 Suda 1451 Sept. 4, 1973 1 FUEL INJECTION SYSTEM FOR INTERNAL COMBUSTION ENGINES Seiji Suda, Hitachi, Japan 3,521,606 7/1970 Schmidt 123/32 EA FOREIGN PATENTS OR APPLICATIONS 1,125,718 3/1962 Germany 123/32 1,939,611 1969 Germany 123/32 Primary ExaminerLaurence M. Goodridge Assistant Examiner-Ronald B. Cox Attorney-Craig, Antonelli and Hill [30] Foreign Application Priority Data ABSTRAQT June 16, 1969 Japan 44/46865 A fuel 1l'l lCtl0l'l system for mternal combustion engines [52] U5. CL [23/32 EA, 23/32 R, 03/139 E wherein two factors determining the fuel quantity de- 51 Int. c1...- F02b 3/00, F02m 39/00 to internal combustion Engine, the 58 Field 61 Search 123/32 EL take manifold vacuum in the engine and the engine rpm are converted into electrical signals having values cor- 56] References Cited responding to those of the intake manifold vacuum and UNITED STATES PATENTS the engine rpm, and the signals as well as a time interval signal (sawtooth wave) generated at the beginning of 31612339 10/ i3 gamazuka 32 fuel injection are applied to the input of a level discrimggig i 3 23 2:12:; 1 ination circuit such that the solenoid valves are held 2644094 6/1953 Douglas 155 EA open up to the time when the sum of the applied signals 2886:015 5/1959 steinkehjw 123/32 EA reaches a discrimination level so as to inject fuel into 2193 744 5 1960 Paule 123 32 EA the internal Combustion engine as a function of time. 2,992,640 7/1961 Knapp 123 32 EA characterized in that the rate of change of the time in- 3,032,025 5/1962 Long 123/32 EA terval signal is varied according to a predetermined 3,051,152 1962 Pauli-m 1231/32 EA time lapse to thereby correct the fuel supply character- 3,338,221 8/1967 5611011.... 123 32 EA 3,429,302 2/1969 Scholl.... 123/32 EA I 3,448,728 6/1969 Scholl 123/32 EA 20 Claims, 14 Drawing Figures TRIGGER SMNA, GEN

UK 5 6 7 1 j a 1 1 l g' g w DISCR/M- AMPL DASTR/BUTOR CK N47 ION 670' C K T CK T vacuum 3 5 DETECWNG 3 Y FUEL /NJEC770N VALVE REVOLUTION LEECWNG PATENTEUSEP 4 ms SHEET 1 0F 4 DbTR/BUWR CKT VALVE AMPL C K T /V calvsm/vr WIPE/IVTERWL S/GNAL GEN CK T VACUUM DETECTING REVULU 7' ION 7(sec) INVENTOR SEIIH SU'DH BY 01mm, um"

ATTORNEYS PATENTED SEP 4 I975 SHEEI 8 BF 4 FIG. 5b

FIG. 50

FIG. 7

FIG. 6

A/(rp m) INVENTOR SEHH SUDH ATTORNEYS put of the time interval signal generating circuit 2 will be higher than the discrimination level of the discrimination circuit prior to the generation of the trigger signal, the discrimination circuit 5 has no output and thus the fuel injection valves 8 remain closed altogether. Now, as the time interval signal is reset by the application of the trigger signal to the time interval sig nal generating circuit 2 in the manner described above, the inputs to the discrimination circuit 5 include only the conditional signals. Thus, if the output characteristics of the both detecting means 3 and 4 are so preset that the sum of these conditional signals will be lower than the discrimination level, the discrimination circuit 5 has an output since the input it receives is lower than the discrimination level, and this output is applied through the amplifier circuit 6 and the distributor 7 to the fuel injection valve 8 which corresponds to the said cylinder on the suction stroke and the injection valve 8 now opens. The simultaneously excited time interval signal increases with the lapse of the injection time, so that when the sum of this signal and the conditional signals reaches the discrimination level of the discrimination circuit 5, the output from the discrimination circuit 5 terminates and the injection valve 8 is closed to complete the fuel injection. In this case, the fuel quantity injected is a function of the duration of opening of the fuel injection valve 8 and moreover this time duration can be controlled, as desired, according to the time rate of change of the time interval signal, the values of the conditional signals and the discrimination level. Thus, by preliminary setting these characteristics in relation with the fuel injection characteristics of an internal combustion engine, the rate of fuel supply can be controlled through the electrical controls.

One of the important factors which determine the fuel quantity to be delivered to an internal combustion engine is the value of a load imposed on the engine. Since the value of this engine loading can be effectively detected in terms of a value of the intake manifold vacuum, the fuel supply characteristics relative to this intake manifold vacuum will now be explained with reference to FIG. 2. Since the fuel quantity delivered is a function of the duration of opening of an injection valve as previously explained, it can be represented by the time duration T of the opening of the fuel injection valve 8. Thus, assuming that the engine rpm N is fixed, the time duration T is generally in inverse proportion to the intake manifold vacuum (mmHg). In other words, the valve open duration T tends to increase as the intake manifold vacuum P is reduced (as it approaches atmospheric pressure P With the engine rpm N being fixed, this intake manifold vacuum is inversely proportional to the throttle valve opening and thus the intake manifold vacuum P may be divided into a high output region, an intermediate output region and a low output region. Here, it is assumed that a region with the wide open throttle valve and a low intake manifold vacuum P (P P P is defined as the high output region, an intermediary region with the throttle valve fairly well opened (P P, P as the intermediate output region, and a region with a slightly opened throttle valve (P P, P, as the low output region. The valve open duration T of the fuel injection valve 8 should preferably be correlated with the intake manifold vacuum P such that the duration T proportionally increases as it nears the high output region with the low intake manifold vacuum P. The reason is that the low intake manifold vacuum P indicates that the throttle valve is opened wide and there is a real need for the generation of high power, so that in this region it is desirable to supply such an amount of fuel as will ensure the maximum output regardless of fuel economy and the like.

This kind of correction is necessary in relation with the engine speed. As shown in FIG. 3, the injection valve open duration T tends to increase as the engine rpm N rises, however the rate of this increase varies depending on the value of the intake manifold vacuum P and therefore the output characteristics of the revolution detecting circuit 4 must be corrected according to the value of the intake manifold vacuum P.

According to the present invention, as shown in FIG. 4, the aforesaid two characteristic corrections can be simultaneously achieved by inflecting the time interval signal I, with respect to the injection duration T at near the time T and time T which correspond to the points of inflection of the output regions relative to the intake manifold vacuum P. In other words, referring to FIGS. 5a and 5b, a discrimination input current I of the discrimination circuit 5, to be described in connection with FIG. 8, has the characteristics as shown in FIG. 5a relative to the vacuum condition signal 1 Assuming that 1,, represents the discrimination level of the discrimination circuit 5, the value (I lp) represents the time interval signal I required to attain the discrimination level I Then, with the time interval signal characteristics shown in FIG. 5b, by inflecting the time interval signal at the time durations T and T corresponding to the points of inflection of the intake manifold vacuum, the fuel injection characteristics as shown in FIG. 2 can be obtained relative to the intake manifold vacuum P, though the vacuum sensitive signal characteristics are straight as shown in FIG. 6. In other words, if it is preset such that the time rate of change of the signal is the maximum during the time interval between the fuel injection starting time T; and time T and then it successively decreases with respect to the time intervals T T T and so on, the fuel injection time duration T tends to be longer as the rate of change of the signal is reduced. Thus, the maximum time duration change can be obtained with respect to the change of the vacuum condition signal [p in the region where the intake manifold vacuum is low (condition signal I I The effect of inflecting the time interval signal described above is also effective with the condition signal I,. representing the engine rpm N, and thus the correction for the engine rpm N can be achieved simultaneously.

If it is necessary that the discrimination circuit 5 discriminate against decreases in the input signals, both the condition signal and the time interval signal may have their polarities reversed.

Referring now to FIG. 8, the electrical connections essential for the construction of the fuel injection system of the type described above will be explained. In the figure, numeral 10 designates a positive plate side power supply line to supply the trigger signal generating circuit 1, the time interval signal generating circuit 2 and the discrimination circuit 5. The trigger signal generating circuit 1 comes into action in synchronism with the engine crankshaft and comprises a switch 12 which is opened concurrent with the beginning of fuel injection, the switch being connected in series with a FUEL INJECTION SYSTEM FOR INTERNAL COMBUSTION ENGINES BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection system for internal combustion engines and particularly to improvements in and relating to a control system by which those engine operating conditions which determine the amount of fuel supply to an internal combustion engine are converted into electrical signals and these electrical signals are then electrically operated to control the solenoid valves (fuel injection valves).

2. Description of the Prior Art The quantity of fuel delivered to an internal combustion engine is governed by the engine operating conditions (such as, engine loading, revolutions per minute and temperature). Accordingly, a system has been known in the prior art in which these various operating conditions are converted into electric conditional signals and the quantity of fuel to be delivered is electrically calculated from these conditional signals to thereby control the fuel injection valves according to the calculated output. A fuel supply system operated on the principle of such an electrical control has been known to have improved fuel supply characteristics as compared with a venturi-type carburetor and a mechanical fuel injection system, and at the same time it provides a useful means to eliminate the problem of the harmful exhaust gases discharged from internal combustion engines. However, the fuel supply characteristics were not necessarily in a simple proportional relationship with the operating conditions of the internal combustion engine, and thus it was necessary to correct the operating condition detecting means, operating means, etc. for a given operating conditional region. Furthermore, there was an inconvenience in that since it was necessary to effect such a correction of the characteristics in consideration of the mutual relationships among the engine operating conditions, the required correcting means tended to be complicated and expensive. Still furthermore, the correction of characteristics by means of mechanical change-over contacts and the like could not ensure smooth correction of the characteristics owing to such adverse effects as a chattering or jumping motion and the hysteresis characteristics at the time of the correction.

SUMMARY OF THE INVENTION A primary object of the present invention is to provide a fuel injection system for internal combustion engines in which the fuel supply characteristics relative to the operating conditions of an internal combustion engine can be readily corrected.

Another object of the present invention is to provide a fuel injection system which is capable of readily achieving the desired fuel supply characteristics.

Still further objects and advantages of the present invention will be apparent from the detailed description of the preferred embodiment taken in conjunction with the accompanying drawings.

The characteristic features of the present invention reside in the fact that in a system wherein there are provided electric conditional signals having values corresponding to the operating conditions of an internal combustion engine and a time interval signal whose value varies in accordance with the passing of time from the beginning of the fuel injection to the engine, and these signals are then applied to operating means to generate an electric output signal having a time width corresponding to the desired amount of fuel supply to thereby control according to this output signal the fuel injection valves for the internal combustion engine, the rate of change of the said time interval signal with respect to the passage of time being varied within a predetermined region.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the fuel injection system for internal combustion engines according to the present invention.

FIG. 2 is a diagram showing the fuel supply characteristics relative to the engine intake manifold vacuum.

FIG. 3 is a diagram showing the fuel supply characteristics relative to the engine rpm.

FIG. 4 is a diagram showing the time duration signal characteristics relative to the passage of time from the beginning of the fuel injection.

FIGS. 5a and 5b are diagrams for explaining the operating characteristics of the operating means.

FIG. 6 is a diagram showing the characteristic of the engine intake manifold vacuum sensitive signal.

FIG. 7 is a diagram showing the characteristics of the engine rpm sensitive signal.

FIG. 8 is a wiring diagram of the system in accordance with the present invention.

FIGS. 9a, 9b, 9c and 9d are diagrams showing the voltage and current waveforms at the various portions of the electric circuit shown in FIG. 8.

FIG. 10 is a diagram showing the characteristics of the level discrimination circuit used in the system of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

Referring to FIG. 1, numeral 1 designates a trigger signal generating circuit adapted to operate in synchronism with the crankshaft to generate a trigger signal at a predetermined fuel injection starting time; 2 a time signal generating circuit adapted to be excited to start operating upon receipt of the trigger signal from the trigger signal generating circuit, 3 a pressure detecting circuit which, in order to detect the loading to be imposed on the internal combustion engine, detects the engine intake manifold vacuum that corresponds to the engine loading so as to generate an electric vacuum condition signal; 4 a revolution detecting circuit for detecting the engine rpm to generate an electric rpm condition signal; 5 a discrimination circuit adapted to receive the said conditional signals at the inputs thereof so as to generate an output when the sum of the received signal is smaller than a predetermined value (discrimination level) and terminate its output when the said sum reaches the predetermined value. It is so arranged that the output from the discrimination circuit 5 is amplified in an amplifier circuit 6, so that the amplified output is distributed by a distributor 7 to fuel injection valves 8 (solenoid-operated type) which may be installed as desired.

With the control system described above, when a given cylinder is on the suction stroke the trigger pulse generating circuit 1 applies a trigger signal to the time interval signal generating circuit 2 to provide a time interval signal. In this case, if it is preset such that the outresistor 11 and disposed between the power supply line and the ground. With the switch 12 being connected to the ground, this series circuit generates a voltage as shown in FIG. 9a across the junction point a between the resistor 11 and the switch 12. This junction point a is connected through a differentiator circuit composed of a capacitor 13 and a resistor 14 to the base electrode of an NPN transistor having its emitter electrode grounded. The collector electrode of this transistor 15 is connected through a resistor 16 to the power supply line 10 and it is also connected to the ground through the intermediary of a capacitor 17 and a diode 18 which is connected in series with the capacitor 17 in the forward direction with respect to the power source, so that a reset signal as shown in FIG. 9b is developed at an anode electrode 1; of the diode 18. The time interval signal generating circuit 2 consists of a sawtooth wave generating circuit employing a bootstrap circuit, in which the collector electrode of an NPN transistor 19 is directly connected to the power supply source 10 and its emitter electrode is grounded through a resistor 20. In the series circuit comprising a diode 21, a resistor 22 and a capacitor 23 which are series-connected in this order from the power supply line 10 to the ground, the junction point between the diode 21 and the resistor 22 is connected through a ca pacitor 24 to the emitter electrode of the transistor 19, while the junction point between the resistor 22 and the capacitor 23 is connected to the base electrode of the transistor 19 and also to the junction point a in the trigger signal generating circuit 1 through the intermediary of a diode 25 connected in the forward direction. Resistors 26, 27 and resistors 28, 29 are respectively connected in series between the power source line 10 and the ground to produce a clamp voltage, and the voltage dividing points of the two series circuits are connected to the junction point of the resistor 22 and the capacitor 23 through diodes 30 and 31 and a resistor 32, respectively. The emitter electrode (junction point C) of the transistor 19 is connected through a resistor 34 to a signal input terminal 35 of the discriminator circuit 5 so as to apply thereto a signal as shown in FIG. 9c. The discrimination circuit 5 comprises a circuit composed of an Esaki diode 36 and an NPN transistor 37. The Esaki diode is connected between the input terminal 35 and the ground in the forward direction with respect to the signal current and the base and emitter electrodes of the transistor 37 are also connected in parallel with the Esaki diode 36 in the forward direction. The collector electrode (a point d) of the transistor 37 is connected to the power supply line 10 via a resistor 38 and to an output terminal 39 to deliver a signal as shown in FIG. 9d. Numeral 40 designates a resistor connected between the input terminal 35 and the power supply line 10, and the Esaki diode 36 is adapted to ensure the valley current to keep the transistor 37 in conduction state. The input terminal 35 is connected to both the engine intake manifold vacuumdetecting circuit 3 and the engine rpm detecting circuit 4, and at the same time it is connected through a diode 41 to the point b in the trigger signal generating circuit 1. The input terminal 35 is also connected through resistor 42 and a capacitor 43 to the power supply line 10, so that when a circuit is closed to the power source, the transistor 37 is rendered conductive to reset the discrimination circuit 5.

In operation, the activation of the power supply 10 supplies a surge current to the input terminal of the discrimination circuit 5 through the resistor 42 and the capacitor 43, so that the discrimination circuit 5 is reset.

In other words, the characteristics of the discrimination circuit 5 as determined by the combination of the Esaki diode 36 and the transistor 37 are now as shown in FIG. 10. With the ordinate representing the current I supplied to the input terminal 35 and the abscissa representing the voltage E, the terminal voltage E of the Esaki diode 36 is, as shown by a curve 36, lower than the operating voltage E of the base-emitter input characteristic curve 37 of the transistor 37 in the area under the maximum value I Therefore, in this area the transistor 37 will be cut off, causing an output signal to appear at the junction point d. Thus, by so setting that the aforesaid surge current that will flow upon closing of the circuit to the power source it now has a value higher than the maximum value I of the Esaki diode 36 and hence the terminal voltage E has a value higher than the operating voltage E of the transistor 37, which is rendered conductive. The terminal voltage E is now represented by a composite characteristic curve 35. Under these conditions, the inflowing current I will not return to the region below the maximum value unless the currentl becomes lower than the valley current I and thus this current is maintained by means of a resistor 40. Of course, the engine vacuum condition signal and the engine rpm condition signal are supplied, from this time, from the detecting circuits 3 and 4, respectively.

Once the engine is in operation and the degree of the crankshaft rotation attains a predetermined fuel injection position, the switch 12 is opened and thus the potential at the junction point a now rises substantially up to the power source voltage as shown in FIG. 9a. As the voltage builds up, a voltage of positive polarity is applied through the capacitor 13 between the base and emitter electrodes of the transistor 15, so that the transistor 15 is driven into conduction and the voltage across its collector electrode now drops almost to ground potential. Before this happens, the capacitor 17 connected to the collector electrode of the transistor 15 has been charged with the polarity as shown from the power supply line 10 through the resistor 16 and the diode l8, and therefore at the same time that the transistor 15 becomes conductive, the potential at the junction point b becomes negative and a trigger signal (negative pulse) as shown in FIG. 9b is generated. This trigger signal reduces through the diode 41 the input current to the discrimination circuit 5 below the valley current I so that the Esaki diode 36 is moved into the region below the maximum value I thus rendering the transistor 37 nonconductive. When the transistor 37 is cutoff, the potential at its collector becomes substantially equal to the power source voltage, and a voltage as shown in FIG. 9d is delivered from the output terminal 39. Accordingly, if this output voltage is amplified and applied to energize an injection valve that is to inject, the injection starts at this moment.

Simultaneously with the opening of the switch 12, the capacitor 23 previously short-circuited by the switch 12 through the diode 25 now starts to charge, so that this voltage rise applies a forward bias voltage to the base electrode of the transistor 19 thereby developing at its emitter electrode (junction point c) a voltage having the form as shown in FIG. 9c. The charging circuitry for the capacitor 23 comprises a first series circuit composed of the diode 21 and the resistor 22, a second series circuit composed of the resistors 26, 33 and the diode 31 and a third series circuit composed of the resistors 28, 32 and the diode 30. Here, if, for example, the setting is made so that the anode voltage of the diode 31 in the third series circuit is made, by the resistor 27, to be equal to that which provides the current I at time T in the FIG. 4, while the anode voltage of the diode 30 in the second series circuit is also made, by the resistor 29, to be equal to that which provides the current I at time T the charging characteristics of the capacitor 23 will be inflected at times T and T as shown in FIGS. 4 and 9c, thereby providing the desired time interval signal I Assuming now that the discrimination level I as determined by the conditional signal current (as supplied from the detecting circuits 3 and 4) for the fuel injection under way is I shown in FIG. 90, at time T at which the time interval signal I corresponding to the value of is generated, the input current to the discrimination circuit 5 reaches the maximum current I of the Esaki diode 36, so that the transistor 37 is rendered conductive and the potential at its collector becomes substantially equal to the ground potential terminating the output terminal voltage (FIG. 9d). At this time the fuel injection valve is closed to terminate the fuel injection.

Since the Esaki diode presents a very small input impedance, the proper setting of the resistor in the time interval signal generating circuit 2 and of the resistors (not shown) in the condition detecting circuits 3 and 4 makes the input current at the input terminal 35 substantially equal to the algebraic sum of the various currents, so that the desired fuel supply be realized by making the conditional signal characteristics have given properties. In other words, since the value of the discrimination level 1,, is reduced as the value of conditional signal current increases, the time required for the time interval signal I, to reach this discrimination level I is shortened with a resultant decrease in the fuel quantity to be injected. The greater the value of the conditional signal current, the more the time is required with a resultant increasein the amount of fuel supply. The rate of change of these factors are corrected at the points of inflection of the time interval signal and this simplifies the construction of the condition detecting means.

In the embodiment described above, no detailed explanation has been made with respect to the specific construction of the vacuum detecting means and the engine rpm detecting means. However, a system in which the displacement of a diaphragm is converted into an electrical signal by means of a variable resistor or a differential transformer may be used for the former means, while a system wherein the conversion into electrical signal is effected by means of a generator (tachometer generator) may be used for the latter means.

Furthermore, while the discrimination circuit explained in conjunction with the description of the preferred embodiment consists of a hybrid circuit comprising an Esaki diode and a transistor, any other means may be selected depending on the kinds of signals (current, voltage etc.) applied thereto. The signals can also be applied in various forms depending on the configuration of the discrimination circuit.

Still furthermore, it is self-evident that the various changes and modifications may be made to the specific circuit configurations without departing from the scope of the invention set forth in the claims.

5 I claim:

1. A fuel injection system for internal combustion engines comprising:

first means for generating a time variable signal having a predetermined characteristic curve representative of a fuel injection time interval with respect to the intake manifold pressure;

second means for producing a voltage signal having an amplitude indicative of a desired fuel injection time interval determined from actually measured engine parameters including at least the engine speed and the intake manifold pressure; and

third means for initiating the generation of said time variable signal simultaneously with the beginning of each cycle of the fuel injection and producing a signal for ending the fuel injection of each cycle when said time variable signal reaches a value equal to the amplitude of said voltage signal.

2. A fuel injection system for internal combustion engines according to claim 1, wherein said first means includes a capacitor charging circuit and means for changing the time constant of said charging circuit to thereby control the rate of change of said time variable signal.

3. A fuel injection system for internal combustion engines according to claim 2 characterized by including a capacitor connected to the power source through a first charging circuit, and at least one further charging circuit connected to said capacitor through a reverse current blocking means and through a voltage dividing circuit divided to a voltage lower than the power source voltage.

4. In a fuel injection system for an internal combustion engine having means, responsive to manifold pressure and the speed of rotation of the engine, for generating first and second control signals respectively representative of said pressure and speed and having fuel injection valves to which fuel is supplied to operate the engine, the improvement comprising:

first means, responsive to the rotation of the engine,

for generating a first electrical signal synchronized with the rotation of the engine, representative of the engine fuel injection starting time;

second means, responsive to the rotation of the engine and being synchronized therewith, for generating a second electrical signal representative of a predetermined function, the characteristics of which vary with respect to time; and

third means receiving the first and second electrical signals, generated by said first, and responsive second means and receiving said first and second control signals, for supplying a fuel injection supply signal to a fuel injection valve in accordance with said first electrical signal and for terminating the generation of said fuel injection supply signal when said second electrical signal reaches a value determined by said first and second signals, whereby the amount of fuel supplied to the engine is controlled in accordance with said predetermined function.

5. A fuel injection system according to claim 4, wherein said second means comprises a segmented linear signal function generator for generating a voltage signal, the characteristics of which are linearly segmented with respect to the lapse of time from the start of the generation of said first signal by said first means.

6. A fuel injection system according to claim 4, wherein said third means comprises a voltage discrimination circuit for comparing the sum of said first and second control signals and said second signal with a prescribed electrical level for terminating said fuel injection supply signal when said sum reaches said prescribed electrical level.

7. A fuel injection system according to claim 6, wherein the second means comprises a segmented linear signal function generator for generating a voltage signal, the characteristics of which are linearly segmented with respect to the lapes of time from the start of the generation of said first signal by said first means.

8. A fuel injection system according to claim 7, wherein said segmented linear signal function generator comprises a first capacitor charging circuit responsive to a source of supply voltage for generating a voltage at the output thereof, the magnitude of which follows said predetermined function.

9. A fuel injection system according to claim 8, wherein said first capacitor charging circuit comprises a plurality of non-linear voltage generating circuits, each of which includes a non-linear current conducting element and a resistor element coupled between said source of supply voltage and a capacitor, across the terminals of which said voltage function is generated.

10. A fuel injection system according to claim 8, wherein said discrimination circuit comprises an Esaki diode and a first transistor having an input, output and control electrode, said Esaki diode being connected in parallel with said input and control electrode of said transistor, said second signal being supplied to the control input of said first transistor and said fuel injection supply signal being taken from the output electrode of said first transistor.

11. A fuel injection system according to claim 9, wherein said discrimination circuit comprises an Esaki diode and a first transistor having an input, output and control electrode, said Esaki diode being connected in parallel with said input and control electrode of said transistor, said second signal being supplied to the control input of said first transistor and said fuel injection supply signal being taken from the output electrode of said first transistor.

12. A fuel injection system according to claim 11, wherein said function generating circuit further includes a boot-strap transistor circuit connected between said capacitor charging circuit and the control electrode of said first transistor.

13. A fuel injection system according to claim 10,

further including a differentiator circuit connected be tween the voltage supply source and the input of said discrimination circuit.

14. A fuel injection system according to claim 12, further including a differentiator circuit connected between the voltage supply source and the input of said discrimination circuit.

15. A fuel injection system according to claim 9, wherein said first means comprises a second capacitor charging circuit, responsive to the rotation of the engine, for generating said first electrical signal in response to the voltage across said second capacitor charging circuit.

16. A fuel injection system according to claim 15, wherein said second capacitor charging circuit comprises a capacitor and a switching circuit responsive to the rotation of the engine for generating a switching voltage to control the charging of the capacitor of said second capacitor charging circuit.

17. A fuel injection system according to claim 16, wherein said discrimination circuit comprises an Esaki diode and a first transistor having an input, output and control electrode, said Esaki diode being connected in parallel with said input and control electrode of said transistor, said second signal being supplied to the con trol input of said first transistor and said fuel injection supply signal being taken from the output electrode of said first transistor.

18. A fuel injection system according to claim 17, wherein said switching circuit comprises an electrical switch connected between said source of supply voltage and a transistor circuit connected across said electrical switch, the output of said transistor circuit being connected to one side of a capacitor for controlling the charging thereof, the other side of said capacitor being coupled to the input of said discrimination circuit.

19. A fuel injection system according to claim 18, further including a differentiator circuit connected between the voltage supply source and the input of said discrimination circuit.

20. A fuel injection system according to claim 18, further including a diode element connected between said electrical switch and the junction of the capacitor of said first capacitor charging circuit and said plurality of non-linear voltage generating circuits. 

1. A fuel injection system for internal combustion engines comprising: first means for generating a time variable signal having a predetermined characteristic curve representative of a fuel injection time interval with respect to the intake manifold pressure; second means for producing a voltage signal having an amplitude indicative of a desired fuel injection time interval determined from actually measured engine parameters including at least the engine speed and the intake manifold pressure; and third means for initiating the generation of said time variable signal simultaneously with the beginning of each cycle of the fuel injection and producing a signal for ending the fuel injection of each cycle when said time variable signal reaches a value equal to the amplitude of said voltage signal.
 2. A fueL injection system for internal combustion engines according to claim 1, wherein said first means includes a capacitor charging circuit and means for changing the time constant of said charging circuit to thereby control the rate of change of said time variable signal.
 3. A fuel injection system for internal combustion engines according to claim 2 characterized by including a capacitor connected to the power source through a first charging circuit, and at least one further charging circuit connected to said capacitor through a reverse current blocking means and through a voltage dividing circuit divided to a voltage lower than the power source voltage.
 4. In a fuel injection system for an internal combustion engine having means, responsive to manifold pressure and the speed of rotation of the engine, for generating first and second control signals respectively representative of said pressure and speed and having fuel injection valves to which fuel is supplied to operate the engine, the improvement comprising: first means, responsive to the rotation of the engine, for generating a first electrical signal synchronized with the rotation of the engine, representative of the engine fuel injection starting time; second means, responsive to the rotation of the engine and being synchronized therewith, for generating a second electrical signal representative of a predetermined function, the characteristics of which vary with respect to time; and third means receiving the first and second electrical signals, generated by said first, and responsive second means and receiving said first and second control signals, for supplying a fuel injection supply signal to a fuel injection valve in accordance with said first electrical signal and for terminating the generation of said fuel injection supply signal when said second electrical signal reaches a value determined by said first and second signals, whereby the amount of fuel supplied to the engine is controlled in accordance with said predetermined function.
 5. A fuel injection system according to claim 4, wherein said second means comprises a segmented linear signal function generator for generating a voltage signal, the characteristics of which are linearly segmented with respect to the lapse of time from the start of the generation of said first signal by said first means.
 6. A fuel injection system according to claim 4, wherein said third means comprises a voltage discrimination circuit for comparing the sum of said first and second control signals and said second signal with a prescribed electrical level for terminating said fuel injection supply signal when said sum reaches said prescribed electrical level.
 7. A fuel injection system according to claim 6, wherein the second means comprises a segmented linear signal function generator for generating a voltage signal, the characteristics of which are linearly segmented with respect to the lapes of time from the start of the generation of said first signal by said first means.
 8. A fuel injection system according to claim 7, wherein said segmented linear signal function generator comprises a first capacitor charging circuit responsive to a source of supply voltage for generating a voltage at the output thereof, the magnitude of which follows said predetermined function.
 9. A fuel injection system according to claim 8, wherein said first capacitor charging circuit comprises a plurality of non-linear voltage generating circuits, each of which includes a non-linear current conducting element and a resistor element coupled between said source of supply voltage and a capacitor, across the terminals of which said voltage function is generated.
 10. A fuel injection system according to claim 8, wherein said discrimination circuit comprises an Esaki diode and a first transistor having an input, output and control electrode, said Esaki diode being connected in parallel with said input and control electrode of said transistor, said second signal being supplied to the cOntrol input of said first transistor and said fuel injection supply signal being taken from the output electrode of said first transistor.
 11. A fuel injection system according to claim 9, wherein said discrimination circuit comprises an Esaki diode and a first transistor having an input, output and control electrode, said Esaki diode being connected in parallel with said input and control electrode of said transistor, said second signal being supplied to the control input of said first transistor and said fuel injection supply signal being taken from the output electrode of said first transistor.
 12. A fuel injection system according to claim 11, wherein said function generating circuit further includes a boot-strap transistor circuit connected between said capacitor charging circuit and the control electrode of said first transistor.
 13. A fuel injection system according to claim 10, further including a differentiator circuit connected between the voltage supply source and the input of said discrimination circuit.
 14. A fuel injection system according to claim 12, further including a differentiator circuit connected between the voltage supply source and the input of said discrimination circuit.
 15. A fuel injection system according to claim 9, wherein said first means comprises a second capacitor charging circuit, responsive to the rotation of the engine, for generating said first electrical signal in response to the voltage across said second capacitor charging circuit.
 16. A fuel injection system according to claim 15, wherein said second capacitor charging circuit comprises a capacitor and a switching circuit responsive to the rotation of the engine for generating a switching voltage to control the charging of the capacitor of said second capacitor charging circuit.
 17. A fuel injection system according to claim 16, wherein said discrimination circuit comprises an Esaki diode and a first transistor having an input, output and control electrode, said Esaki diode being connected in parallel with said input and control electrode of said transistor, said second signal being supplied to the control input of said first transistor and said fuel injection supply signal being taken from the output electrode of said first transistor.
 18. A fuel injection system according to claim 17, wherein said switching circuit comprises an electrical switch connected between said source of supply voltage and a transistor circuit connected across said electrical switch, the output of said transistor circuit being connected to one side of a capacitor for controlling the charging thereof, the other side of said capacitor being coupled to the input of said discrimination circuit.
 19. A fuel injection system according to claim 18, further including a differentiator circuit connected between the voltage supply source and the input of said discrimination circuit.
 20. A fuel injection system according to claim 18, further including a diode element connected between said electrical switch and the junction of the capacitor of said first capacitor charging circuit and said plurality of non-linear voltage generating circuits. 